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Re: Bug#370471: use of "invoke-rc.d $PACKAGE stop || exit $?" in prerm scripts

On Wed, 21 Jun 2006, Gerrit Pape wrote:
> On Mon, Jun 05, 2006 at 03:36:30PM +0300, Lars Wirzenius wrote:
> > The policy manual says (9.3.2 Writing the scripts):
> > 
> >         The init.d scripts should ensure that they will behave sensibly
> >         if invoked with start when the service is already running, or
> >         with stop when it isn't, and that they don't kill
> >         unfortunately-named user processes.
> > 
> > Would it be acceptable to change this to say "must ensure"?
> You might call this nitpicking, but with the current Debian init scripts
> using start-stop-daemon, this isn't really achievable.  See the
> start-stop-daemon(8) man page:

You should use start-stop-daemon with both --name AND --pidfile together
(never use --exec unless you REALLY know you will always stop the daemon
before it changes on disk) in an initscript.  That changes start-stop-daemon
into a homing killall.

> And relying on a pidfile also doesn't guarantee that ``they don't kill
> unfortunately-named user processes'', but actually can cause exactly
> that, AFAICT.

Nothing is 100% foolproof, of course.  --exec is damn good at homing exactly
on what you want, but you'd need to know the inode of the already unlinked
executable if it is restarted after being upgraded.  Hints are welcome, so
far we got far more breakage from --exec than any benefits.

A pidfile + process name check is actually quite good enough in practice,
IME.  I have never seen it misfire in my life other than in fabricated

Of course, bird-brain interpretors like python in which it is hell to change
the process name and on top of it insist on running all scripts/programs
with the interpretor name sort of widen the error window a lot more than
necessary.  Hints on how to fix that are very welcome, I have at least one
package which would benefit from this.

  "One disk to rule them all, One disk to find them. One disk to bring
  them all and in the darkness grind them. In the Land of Redmond
  where the shadows lie." -- The Silicon Valley Tarot
  Henrique Holschuh

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